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Friday, February 16, 2018 - 15:00 ,
Location: Skiles 271 ,
Yian Yao ,
GT Math ,
Organizer: Jiaqi Yang

I
will report on the parameterization method for computing normally
hyperbolic invariant tori(NHIT) for diffeomorphisms. To this end, a
Newton-like method for solving the invariance equation based on the
graph transform method will be presented with details.
Some notes on numerical implementations will also be included if time
allows.
This is a work by Marta
Canadell and Alex Haro.

Friday, February 9, 2018 - 15:00 ,
Location: Skiles 271 ,
Joan Gimeno ,
BGSMath-UB ,
Organizer: Jiaqi Yang

We are going to explain how invariant dynamical objects, such as (quasi)periodic orbits, can numerically be computed for Delay Differential Equations as well as their stability. To this end, we will use Automatic Differentiation techniques and iterative linear solvers with appropiate preconditioners. Additionally some numerical experiments will be presented to illustrate the approaches for each of those objects.This is joint work with A. Jorba.

Friday, February 2, 2018 - 15:00 ,
Location: Skiles 271 ,
Gladston Duarte ,
University of Barcelona & GT ,
gladston@maia.ub.es ,
Organizer: Jiaqi Yang

In a given system of
coordinates, the Restricted Three-Body Problem has some interesting
dynamical objects, for instance, equilibrium points, periodic orbits,
etc.
In this work, some connections between the stable and unstable manifolds
of periodic orbits of this system are studied. Such connections let one
explain the movement of Quasi-Hilda comets, which describe an orbit
that sometimes can be approximated by an ellipse of semi-major axis
greater than Jupiter's one, sometimes smaller.
Using a computer algebra system, one can compute an approximation to
those orbits and its manifolds and investigate the above mentioned
connections.
In addition, the Planar Circular model is used as a base for the fitting
of the orbit of comet 39P/Oterma, whose data were collected from the
JPL Horizons system. The possibility of using other models is also
discussed.

Friday, November 17, 2017 - 15:00 ,
Location: Skiles 154 ,
Bhanu Kumar ,
GT Math ,
Organizer:

This lecture will discuss
the stability of perturbations of integrable Hamiltonian systems. A
brief discussion of history, integrability, and the Poincaré
nonintegrability theorem will be followed by the proof of the theorem of
Kolmogorov on persistence of
invariant tori. Time permitting, the problem of small divisors may be
briefly discussed. This lecture wIll follow the slides from the
Satellite Dynamics and Space Missions 2017 summer school held earlier
this semester in Viterbo, Italy.

Friday, November 10, 2017 - 14:00 ,
Location: Skiles 154 ,
Rafael de la Llave ,
GT Math ,
Organizer: Jiaqi Yang

We consider Hamiltonian systems with normally hyperbolic manifold with a homoclinic connection. The systems are of the form H_0(I, phi, x,y) = h(I) + P(x,y) ,where P is a one dimensional system with a homoclinic intersection. The above Hamiltonian is a standard normal form for near integrable Hamiltonians close to a resonance. We consider perturbations that are time dependent and may be not Hamiltonian. We derive explicit formulas for the first order effects on the stable/unstable manifolds. In particular, we give sufficient conditions for the existence of homoclinic intersections to the normally hyperbolic manifold. Previous treatments in the literature specify the types of the unperturbed orbits considered (periodic or quasiperiodic) and are restricted to periodic or quasi-periodic perturbations. We do not need to distinguish on the perturbed orbits and we allow rather general dependence on the time (periodic, quasiperiodic or random). The effects are expressed by very fast converging improper integrals. This is joint work with M. Gidea. https://arxiv.org/abs/1710.01849

Friday, November 3, 2017 - 15:00 ,
Location: Skiles 154 ,
Hassan Attarchi ,
Georgia Tech ,
Organizer:

This presentation is about the results of a paper by L. Bunimovich in
1974. One considers dynamical systems generated by billiards which are
perturbations of dispersing billiards. It was shown that such dynamical
systems are systems of A. N. Kolmogorov (K-systems), if the perturbation
satisfies certain conditions which have an intuitive geometric
interpretation.

Friday, October 27, 2017 - 15:00 ,
Location: Skiles 154 ,
Hassan Attarchi ,
Georgia Tech ,
Organizer:

This presentation is about the results of a paper by Y. Sinai in
1970. Here, I will talk about dynamical systems which resulting from the
motion of a material point in domains with strictly convex boundary,
that is, such that the operator of the second quadratic form is
negative-definite at each point of the boundary, where the boundary is
taken to be equipped with the field of inward normals. It was proved
that such systems are ergodic and are K-systems. The basic method of
investigation is the construction of transversal foliations for such
systems and the study of their properties.

Friday, October 13, 2017 - 15:00 ,
Location: Skiles 154 ,
Bhanu Kumar ,
GT Math ,
Organizer: Jiaqi Yang

Birkhoff's Theorem is a result useful in characterizing the boundary of certain open sets U ⊂ T^1 x [0, inf) which are invariant under "vertical-tilting" homeomorphisms H. We present the method used by A. Fathi to prove Birkhoff's theorem, which develops a series of lemmas using topological arguments to prove that this boundary is a graph.

Friday, October 6, 2017 - 15:00 ,
Location: Skiles 154 ,
Sergio Mayorga ,
Georgia Tech ,
Organizer: Jiaqi Yang

We will look at a system of hamiltonian equations on the torus, with an
initial condition in momentum and a terminal condition in position, that
arises in mean field game theory. Existence of and uniqueness of
solutions will be shown, and a few remarks will be made in regard to its
connection to the minimization problem of a cost functional. This is the second part of lasrt week's talk.

Friday, October 6, 2017 - 15:00 ,
Location: Skiles 154 ,
Prof. Rafael de la Llave ,
School of Mathematics, Georgia Tech ,
Organizer: Jiaqi Yang

We will present an introduction to the results of S. Aubry and J. Mather who used variational methods to prove the existence of quasi-periodic orbits in twist mappings and in some models appearing in solid state Physics.